Method of producing a container

ABSTRACT

A method of producing a container of plastic material capable of being oriented and/or crystallized, in which a substantially tubular blank is, in at least two mutually consecutive and mutually separate shaping phases or shaping stages, reshaped into the container. The blank is reshaped into the container by mechanical forming elements (34,42) which stretch the material in the axial direction of the blank, and in the circumferential direction of the blank. By stretching the material in each separate shaping stage to a regulated degree, there will be accumulated in the material a total stretching corresponding to the requisite stretching in order to impart to the material the desired and predetermined orientation and thereby the requisite strength properties.

FIELD OF THE INVENTION

The present invention relates to a method of producing a container froma tubular blank of plastic material capable of being oriented and/orcrystallized, in at least two consecutive shaping stages, utilizingmechanical forming elements for stretching the material in the axialdirection of the blank and in the circumferential direction of theblank.

PRIOR ART

It is previously known in this art to reshape blanks, which includeaxially oriented material, into containers. In such a process, thereshaping is effected by means of a blowing process in which the blankis brought into abutment against forming walls whose form(configuration) corresponds to the form of the container which is to beproduced. Patent Specification No. GB 2 076 731 describes a techniquefor the production of a bottle-like container from a blank whichincludes axially oriented material.

Patent Specification No. GB 2 052 364 discloses a technique in which anaxially stretched blank is, by one or more mechanical reshaping stages,reshaped into a container. According to the technique shown in thisPatent Specification, a reduction only of the circumference of thecontainer body takes place on reshaping of the blank into the container.

Patent Specification No. GB 2 052 363 describes a technique in which ablank of axially oriented material is reshaped, by a blowing process,into a container. Also according to this patent specification, anaxially oriented blank is reshaped into a container.

There are pressing needs within this Art for a container of plasticmaterial which is suitable for high-temperature applications and/or forthe storage of liquids under pressure, e.g. the storage of carbonatedsoft drinks, beer etc. The term high-temperature application is heretaken to mean that the containers are used, for example, forpasteurization (at 60°-65° C.) of the contents in the filled and sealedcontainer, for hot-filling, by which is taken to mean that boilingliquid is filled directly into the containers, or for sterilization (atleast 121° C.) of the contents of the filled and sealed containers.

Further desires relating to containers of plastic material are that itmust be possible to produce containers whose body is of a cross sectionwhich is independent of the mouth portion of the container, e.g. thebody has a polygonal cross section, while the mouth portion of thecontainer is circular. The circular configuration of the mouth portionof the container is desirable so as to facilitate closure of thecontainer.

So as to reduce unit costs for the containers, it is further necessarythat the material distribution in the containers be adapted to meetcalculated mechanical stresses in the different parts of the container(mouth portion, container body and bottom). Furthermore, it is alsonecessary that the material distribution in each region (portion) of theindividual container be as uniform as possible, since the thinnest--andthereby the weakest--part in each such region is determinative of thosestresses which the container can withstand. Apart from the materialdistribution, the mechanical strength of the containers is, naturally,also determined by the orientation and/or thermal crystallization of thematerial.

A further requirement placed on containers of the type contemplatedherein, and particularly on containers intended for high-temperatureapplications, is that the shrinkage which occurs on heating of stretchedand oriented material must be eliminated or reduced to acceptablelevels.

In the storage of liquids under pressure, it is a matter of the Laws ofPhysics that when there is inner pressure within the container, its wallmaterial is subjected to a stress which is approximately twice as greatin the circumferential direction as in the axial direction. In order toimprove the strength of the plastic material, it is known in the art toshape the container by a blowing process, the temperature of thematerial being adapted to suit the properties of the material beingemployed in order, during the blowing process, to stretch the materialand thereby orientate it.

The blow molding technology suffers from the drawback that the materialdistribution on shaping of the container is not fully under control,since, on expansion of the blank into the form of the container, it isnot possible to exactly determine and control where and how thestretching and thereby the orientation of the material take place.Normally, the stretching commences at a number of starting points whosepositions are determined by the prevailing temperature distribution inthe material and the stretching forces arising therein. The extent ofthe expansion and the thus obtained stretch relationship is, moreover,temperature-dependent, which, together with the heating of the materialwhich takes place when the material crystallizes in consequence of thestretching, results in that the formed container has a materialthickness which varies, i.e. in one section at right angles to the axialdirection the thickness of the container wall varies in thecircumferential direction. Corresponding variations also occur in theaxial direction of the container, i.e. in axial sections through regionsof substantially the same circumference there are alternatingly thinnerand thicker material portions. Thus the prior art techniques call for aselection of the wall thickness of the blank with reference to theabove-described uncertainty in the stretching and thinning of thematerial, which entails an over-dimensioning of the blank and, thereby,also a material surplus in the formed container.

In order to realize temperature stability in containers of thermoplasticmaterial capable of being oriented and/or crystallized, it is known inthe art to render the containers thermally stable by causing, duringblowing of the containers, the container material to meet hot moldingwalls, against which the material abuts for a relatively long period oftime (of the order of magnitude of 1-2 minutes). This is attained inthat an inner pressure is maintained within the blown container andurges the wall material against the molding walls. However, the longcycle times involved render this technique extremely costly.

SUMMARY OF THE INVENTION

The present invention relates to a technique in which the above-outlineddrawbacks are obviated. According to the present invention, the startingpoint is a blank of material capable of being oriented and/orcrystallized. From the blank is produced a container of high mechanicalstrength and thermal stability, and with improved material distributionas compared with prior art techniques. According to the presentinvention, the time consumed for the production of each individualcontainer is reduced in comparison with the time consumed in prior arttechniques, the present invention also entailing a simplified structure.

Thus, employment of the present invention will bring about a reductionof the requisite material requirement in each container, an attainmentof desired thermal stability and a reduction of costs as compared withprior art techniques currently in use.

According to the present invention, a blank of a thermoplastic materialwhich has the property of being able to be oriented by a mechanicalprocessing and/or to be thermocrystallized by a heat treatment, isreshaped into a container in a number of consecutive reshaping stageswhich, in one preferred embodiment, take place in mutually separatesubstages. In each such phase or stage, the material is stretched eitherin the axial direction or in the circumferential direction of the futurecontainer. By stretching the material each time to a regulated andcontrolled extent, there will be accumulated in the material a totalstretching which corresponds to the stretching required to impart to thematerial the desired and predetermined orientation, and thereby therequisite strength properties.

In one preferred embodiment of the present invention, the blank isreshaped, in all substages, into the container by the use of mechanicalforming elements. The mechanical stretching is effected in each stagewith the material at a determined and regulated temperature which may beselected within a broad range, the temperature selection being, however,determined by the special effect it is desired to attain in thecurrently topical shaping stage under consideration. For materials witha distinct glass transition temperature, hereafter abbreviated as TG,for example the temperature of the material at certain--and as a rule atthe initial--shaping stages is lower than TG, while at the final shapingstage or stages, the temperature as a rule exceeds TG. For the materialpolyethylene terephthalate, hereafter abbreviated to PET, thetemperature, in one preferred embodiment of the present invention, isselected in the range of between 70° and 160° C. for the final shapingstages, while the initial shaping stages generally take place at a lowertemperature.

In certain embodiments of the present invention, the container is givenits final form in a concluding blow molding stage. In this stage, only aminor change of shape will take place in the form of an expansion in thecircumferential direction, e.g. of the container body, so as to producethe desired cross section (e.g. polygonal), while retaining the circularconfiguration and diameter of the mouth portion.

In a first application of the present invention, the point of departureis a cylindrical blank of material with the properties stated above,e.g. a thermoplastic material such as PET. The blank has a bottomportion of a shape which substantially corresponds in its central bottompart to the shape of the central bottom part of the container which isunder production. In a first shaping stage, the material is stretched bymeans of a draw ring which surrounds the blank and cooperates with aninternal mandrel, in the axial direction of the blank. The dimensions ofthe mandrel and the surrounding draw ring are selected such that thereis formed, between the mandrel and the draw ring, a gap, whose width isless than the thickness of the material of the blank. The stretching iseffected in that relative displacement takes place between the draw ringand mandrel, with the result that the material in the blank wall isforced to pass through the gap, whereby the material thickness in thatportion of the blank wall which passes through the gap is reduced, withsimultaneous axial stretching of the blank. As a rule, the thicknessreduction corresponds to that reduction imparted to the material on freestretching, which corresponds to material flow at the temperatureemployed. In this stage, a first preform is created which, inconjunction with its central bottom part, has a region with axiallystretched material. In, for example, Patent Specification No. GB 2 092943, is described a technique for stretching and orienting of plasticmaterial by causing the material to pass through a gap.

In the next stage, the circumference of the body of the first preform iswidened, this body essentially corresponding to the cylindrical portionof the first preform, in that a mandrel is urged into the first preform,the material in the first preform undergoing a certain stretching in thecircumferential direction during simultaneous reduction of the materialthickness. Here, there will be formed a second preform. Those parts ofthe mandrel which widen the first preform most proximal its centralbottom part have, in an axial section, a profile length substantiallycorresponding to the length of the axially stretched material accordingto the preceding paragraph. The transition between the axially stretchedmaterial and the non-axially stretched material constitutes, in thewidened first preform--i.e. in the second preform--the defining line ofthe cylindrical portion of the second preform most proximal the bottomportion.

The material of the cylindrical portion of the second preform isthereafter stretched in an axial direction (with the application of atechnique corresponding to that described above) by means of a draw ringwhich, in cooperation with an internal mandrel, forms a gap. Here, theinternal mandrel is preferably the same mandrel which realized thewidening of the first preform as described in the preceding paragraph.On stretching, the material thickness is reduced during simultaneousaxial elongation of the second preform. As a rule, the thicknessreduction which the material undergoes corresponds to the reductionimparted to the material on free stretching corresponding to materialflow at the temperature employed. Here, there will be created anintermediate preform whose bottom portion substantially has itscounterpart in the material in the bottom portion of the blank and whichotherwise consists of high-grade axially stretched material which, thisapart, has a certain if albeit lesser stretching in the circumferentialdirection of the intermediate preform.

By means of a mandrel which is urged into the intermediate preform, thispreform is further widened for further stretching of the material in thecircumferential direction, so as to attain the material orientaiionwhich provides the requisite strength properties. The reshapingdescribed in this passage is generally effected with the mandrel at araised temperature for shrinking in the axial direction of the blank ofthe stretched material during simultaneous thermocrystallization of thematerial. The term shrinking is here taken to mean the length reductionwhich the stretched material undergoes as a result of the heating. Inthis shaping stage, the intermediate preform is reshaped into a finalpreform. In certain applications, the final preform also constitutes thecontemplated finished product, i.e. constitutes the container proper,while in other applications, the mouth portion of the final preform isreshaped in adaptation to serve its intended purpose, e.g. by means ofmechanical devices it is given a "neck-in" which is required in orderthat a cap, e.g. fixedly-folded with the mouth flange shall not protrudebeyond the container body. In those examples where the body of the finalpreform has a polygonal cross section, the mouth portion is, as a rule,reshaped so as to realize a circular opening.

The nature of the present invention and its aspects will be more readilyunderstood from the following brief description of the accompanyingdrawings, and discussion relating thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompamying drawings:

FIG. 1 is an axial section through a blank placed in an apparatus foraxial orienting of material;

FIG. 2 is an axial section through a preform formed by the blank of FIG.1;

FIG. 3 is an axial section through a widened preform, together withapparatuses for the widening of the preform and axial stretching of thematerial in the preform;

FIG. 4 shows the intermediate preform obtained on the stretchingaccording to FIG. 3;

FIG. 5 is an axial section through the intermediate preform, togetherwith apparatuses for the reshaping of the intermediate preform into afinal preform;

FIG. 6 is an axial section through the reshaped intermediate preform;

FIG. 7 is an axial section through a container;

FIG. 8 is an axial section through a blank of other configuration thanthe blank of FIG. 1;

FIG. 9 is an axial section through the blank of FIG. 8, widened into apreform;

FIG. 10 is an axial section through the blank stretched to anintermediate preform; and

FIG. 11 is an axial section through a final preform obtained byreshaping of the intermediate preform of FIG. 10.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the Drawings, FIG. 1 shows a blank 1 with a tubular blankbody 2 and a closed bottom 3. The blank consists of plastic materialcapable of being oriented and/or crystallized and is, for example,produced by injection molding or thermoforming. Within the blank, thereis a mandrel 30 which is disposed for cooperation with a draw ring 20provided outside the blank. In the mandrel and the draw ring,respectively there are channels 31 and 21, respectively, for atemperature-regulating liquid.

The mandrel 30 and the draw ring 20 are disposed for axial movement inrelation to one another, there being formed a circumferential gap orspace between the mandrel and the draw ring. The width of the gap isadapted to the thickness of the material wall in the blank body 2, inorder, on movement of the draw ring in the direction of the arrows A inrelation to the mandrel 30, to reduce the material thickness of theblank body in a transitional zone between thinner and thicker material,during simultaneous stretching and orienting of the material when thetransitional zone is moved towards the mouth portion of the blank.

FIG. 2 shows one embodiment in which the material is stretched only in alimited region in conjunction with the bottom portion of the blank,there being formed a first preform 10 as shown in FIG. 2.

FIGS. 3 and 4 illustrate a mandrel 32 provided withtemperature-regulating channels 33. The mandrel is of greatercircumference than the circumference of the previously-mentioned mandrel30, and, moreover, the mandrel 32 has, in the transition to its bottomportion, a part curved inwardly towards the center, whose length in theaxial direction of the mandrel corresponds to the length of the axiallystretched material portion of the first preform 10. A mold bottom 40,also provided with temperature-regulating channels 41, is to be found atthe bottom in the Figure. The mold bottom 40 is of a configuration whichcorresponds to the form of the bottom 3. The Figure also shows a drawring 22 with temperature-regulating channels 23. The draw ring 22 isdimensioned so as to form, between itself and the mandrel 32, a gapwhich is moved in a direction towards the mouth portion of a widenedpreform 11 on movement in the direction of the arrows B in relation tothe mandrel 32. On insertion of the mandrel 32 into the first preform 10the widened preform (second preform) is formed and on subsequentmovement of the gap, the material of the body of the widened preform isstretched and oriented in accordance with that disclosed in conjunctionwith FIG. 2, during simultaneous axial elongation of the preform forforming an intermediate preform 12 (FIG. 4). In FIG. 4, the draw ring 22is shown in a position where all material in the blank body 2 hasundergone axial stretching and orienting. The gap 25 formed between themandrel and the draw ring is also apparent in this Figure.

Thus, the function of the mandrel 32 is first to cooperate with the moldbottom 40 on the expansion of the widened preform into the intermediatepreform 12, and secondly to cooperate with the draw ring 22 so as toform the gap 25 through which the material of the container body haspassed so as to attain the desired axial stretching of the material.

FIGS. 5 and 6 show elements for reshaping the intermediate preform 12into the final preform 13. The Figures show a mandrel 34 provided withchannels 35 for temperature-regulating liquid, and with one channel 36for a pressure medium. The channel 36 for the pressure medium dischargesin the bottom portion 37 of the mandrel, where the mandrel is of aconfiguration which is adapted in conformity with the configuration ofthe bottom 3 of the blank.

FIG. 5 also shows an outer support member 42 which surrounds theintermediate preform 12 during its reshaping and which has a centralcavity 44 through which the intermediate preform 12 and the mold bottom40--now operating as a press plunger--pass. In the upper region of thesupport member (with the orientation as shown in FIG. 5), the centralcavity flares so as to form, between the inner defining surface of theouter support member and the outer defining surface of the mandrel 34, agap or space through which the wall of the intermediate preform passeson its reshaping into the final preform 13. For purposes of clarity, theouter support member 42 has been omitted from FIG. 6. In certainapplications, the liquid temperature-regulating channels 43 are used forregulating the temperature of the outer support member 42.

On reshaping of the intermediate preform 12 to the final preform 13, theintermediate preform is placed within the central cavity 44 of the outersupport member and is pressed by the mold bottom 40 in a directiontowards the mandrel 34. Since the mandrel 34 is of a greatercircumference than the inner circumference of the intermediate preform12, the mouth edge of the intermediate preform is urged into abutmentagainst the outer surface of the mandrel 34 and is moved, on continuedupward movement of the mold bottom 40, outwardly and upwardly in theFigure, with simultaneous stretching of the material in thecircumferential direction of the intermediate preform. The abutment ofthe plastic material of the preform against surfaces of the mold bottom40, the outer support member 42 and of the mandrel 34 regulates thetemperature of the plastic material before, during and after thereshaping of the intermediate preform into the final preform. Tostabilize the intermediate preform mechanically, a pressure medium isapplied through the channel 36 to the interior of the intermediatepreform. During the upwardly-directed movement of the intermediatepreform, pressure medium passes between the inner wall of theintermediate preform and the mandrel 34, and thereby reduces thefriction between the plastic material and the inner defining surface ofthe outer support member 42. Once movement is completed, the mold bottom40 assumes the position illustrated in FIG. 6, in which the intermediatepreform is reshaped into the final preform 13. In certain embodiments ofthe present invention, the inner pressure will ensure that the materialis brought into abutment against the outer support member at least inthose regions where reshaping is about to take place.

In certain applications, a reduction of the circumference of the mouthportion then takes place, there being also formed a flared flangeintended to be folded together with a cap or seal once the container hasbeen filled with its final contents.

In certain applications, the mandrel 32 is also provided with acounterpart to the pressure medium channel 36, for cooperation withouter members corresponding to that described in conjunction with FIGS.5 and 6.

FIGS. 8-11 show an alternative embodiment of the present invention. Thefigures illustrate axial sections of the blank 1a during its reshapinginto the container, while, on the other hand, only some of the devices,(mandrel, mold bottom, support member, etc.) which are required inconjunction with the reshaping, are shown. However, these devices,correspond fundamentally to those already described and it will beobvious to the skilled reader of this specification that thepreviously-described devices are, after certain adaptation, alsosuitable for use in this embodiment of the invention.

The blank 1a shown in FIG. 8 is reshaped to the widened preform 11a inthat a mandrel 32a corresponding to the previously described mandrel 32is urged down into the blank which is simultaneously supported by acup-like mold bottom 45. By means of draw rings 22a, the material isthereafter stretched in the axial direction of the blank, anintermediate preform 12a being formed. This is thereafter widened in itscircumferential direction by means of a technique corresponding to thatdescribed in conjunction with FIGS. 5 and 6, to reshape the intermediatepreform 12a into the final preform 13a. By means of thermoformingbetween a die 46 and the mandrel 34a, the bottom portion 18a of theintermediate preform is reshaped to a form corresponding to the form ofthe central bottom part of the bottom portion 16 of the container.Reshaping of the final preform 13a into the container 14 takes place incomplete agreement and correspondence with the previous description andgenerally in the stage when the intermediate preform is reshaped to thefinal preform.

It will be clearly apparent from the body of this description that, incertain applications, the shaping, as illustrated in FIG. 2, of thefirst preform 10 is not used, but that the blank 1 has a circumferencewhich is adapted to orienting the material as described in thediscussion in conjunction with FIG. 3.

All drive means which realize the movements of the mechanical elementshave been omitted from the Drawings. It is obvious to the skilled readerof this specification that these may be arranged and provided accordingto prior art techniques, e.g. such as mechanical, hydraulic or pneumaticdrive means.

The temperature of the material is set and adjusted as required andintended for in each shaping and processing stage by means of thetemperature-regulating liquid channels 21,23,31,33,35,41,43 of themechanical elements. It will also be apparent from this description thatseparate parts of the shaping apparatus are, if necessary, adjustable todifferent temperatures at each individual processing occasion or stage.

As has already been mentioned, the blank is expanded in itscircumferential direction, for stretching of the material in the wall ofthe blank. For materials with a distinct TG, at least the axial, andalso the final stretchings, are generally effected at a temperature inexcess of TG. For, for example, PET, stretching generally takes place inthe temperature range of between 70° and 130° C. In certain embodiments,the expansion in the circumferential direction is effected in one singlereshaping stage, whereas, in other embodiments, in which a greaterdegree of stretching is contemplated, the expansion takes place inseveral consecutive reshaping stages. It generally applies that at leastthe final shaping stage takes place, as a rule, at a raised temperaturein order to thermocrystallize the plastic material.

By means of the mechanical reshaping process the stretching anddistribution of the material is exactly controlled both in the axial andcircumferential direction of the blank or preform and also exactlycontrolled in each forming step. The final product will thus in eachregion (portion) possess a thickness, an orientation and/or acrystallization adapted to the expected stresses in each specific regionof the product. In contrary to a prior Art container, a container madeaccording to the method now presented has, as an example,circumferential material sections at right angles to the axial directionof the container, the sections consisting of material of uniformthickness, orientation and/or crystallization. The term crystallizationis related to the crystallization produced by stretching and/or byheating the plastic material.

In certain embodiments of the present invention, an outer coating isapplied onto the material, for example a barrier material preventing thepassage of light, radiation and/or gas, decorative artwork, etc., inconjunction with that stage in which the intermediate preform isreshaped into the final preform. In this instance, at least the surfacematerial of the intermediate preform is rapidly heated, for example by aso-called flame treatment, whereafter the outer surface of theintermediate preform is provided with the desired coating, e.g. byimmersion dipping, by spraying, by roller coating, etc. The thus treatedintermediate preform is subsequently pre-dried, e.g. when PET is used,preferably at a temperature in the range of between 50° and 60° C.,whereafter the thus treated intermediate preform undergoes theabove-described mechanical reshaping into the final preform. Themechanical reshaping into the preform is preceded, in certainapplications, by a temperature conditioning of the material of theintermediate preform. However, as a rule, such temperature conditioningis concentrated at the bottom portion of the intermediate preform, inorder, in those applications in which the bottom portion of theintermediate preform is reshaped on forming of the final preform, tofacilitate reshaping of the bottom portion.

A considerable advantage inherent in the above-described technique isthat mechanical elements control and determine, on forming of thecontainer, the stretching and the thickness reduction of the material ineach individual material portion and at each individual shaping stage.The employment of an internal mandrel against which the material abutsalso ensures a reliable and rapid thermal adjustment of the material tothe temperature determined for each individual shaping stage. Inparticular in the final shaping stages, the abutment against theinternal mandrel makes for an extremely short material temperatureadjustment time, e.g. for shrinking and/or thermal crystallization ofthe material, since the wall thickness in the final shaping stages isreduced. By combining this inner temperature regulation with atemperature regulation acting against the outer surface of the material,e.g. heating or cooling, the temperature adjustment time will be furtherreduced.

The above-described flame treatment of the material imparts to thesurface layer an excellent adhesion capability of the applied layer. Anypossible subsequent pre-drying in combination with possible temperatureconditioning of the intermediate preform prior to its reshaping into thefinal preform, and the above-described shrinking together with thermalcrystallization of the final preform all make for a reliable adhesion ofthe applied layer.

The above detailed description relates only to a limited number ofembodiments of the present invention, but the skilled reader of thisspecification will readily perceive that the invention accomodates agreat number of modifications in the disclosed embodiments, withoutdeparting from the spirit and scope of the appended Claims.

I claim:
 1. A method of producing a container from a tubular blankhaving a closed bottom at one end and an open mouth at the other end,the blank consisting of plastic material capable of being deformed, saidmethod comprising:axially stretching a limited region of the wall of thetublular blank near said closed bottom end, then circumferentiallystretching a portion of the wall of the tubular blank which extends fromthe open mouth thereof while keeping the closed bottom and an adjacentportion of the wall unstretched, then axially stretching said blank toproduce axial orientation in the wall of said blank, then supporting thetubular blank in an outer support member with the closed bottom of thetubular blank resting on a mold bottom member, positioning a mandrel atthe open mouth of the tubular blank, the mandrel having an outerdiameter which is greater than the inner diameter of the tubular blank,and producing relative movement between the mold bottom member, on theone hand, and the outer support member and mandrel, on the other hand,to force the tubular blank to expand on the mandrel and pass through agap formed between the mandrel and the outer support member whereby tocircumferentially expand the tubular blank to form the container.
 2. Amethod as claimed in claim 1 comprising heating the material such thatthe material is at the temperature of crystallization when the materialpasses through said gap.
 3. A method as claimed in claim 2 wherein theexpanded material of the tubular blank which forms the wall of thecontainer travels on the mandrel as the blank is expanded, said methodfurther comprises heating the wall of the container from the mandrel asthe wall travels on the mandrel.
 4. A method as claimed in claim 1comprising heating the closed bottom of the tubular blank by said moldbottom member during the circumferential expansion.
 5. A method asclaimed in claim 1 comprising pressurizing the interior of the hollowtubular blank during circumferential expansion thereof to reducefriction of the material of the surfaces of the outer support member andthe mandrel.
 6. A method as claimed in claim 5 wherein the pressurizingof the interior of the hollow, tubular blank is effected by conveying apressure medium through a channel in the mandrel to said interior.
 7. Amethod as claimed in claim 5 comprising heating said outer member andcontacting the wall at the tubular blank with the heated outer memberprior to circumferential expansion thereof.
 8. A method as claimed inclaim 7 wherein the outer member is heated to the temperature ofcrystallization of the plastic material.
 9. A method as claimed in claim2 wherein the expanded material of the tubular blank which forms thewall of the container travels on the mandrel as the blank is expanded,said method further comprises heating the wall of the container while onsaid mandrel.
 10. A method as claimed in claim 9 wherein said heating ofthe wall of the container is a flame treatment.
 11. A method as claimedin claim 1 wherein said axial orientation corresponds to that obtainedby stretching of the material to produce material flow.
 12. A method asclaimed in claim 11 wherein said axial stretching is produced by axiallyrelatively moving a draw ring surrounding said tubular blank and aforming body inserted into said blank.
 13. A method as claimed in claim1 wherein said axial stretching is effected only on thecircumferentially stetched portion.
 14. A method as claimed in claim 1comprising applying a barrier coating onto the axially stretchingtubular blank before the blank is circumferentially expanded to form thecontainer.
 15. A method as claimed in claim 14 comprising heating thethus coated blank before the blank is circumferentially expanded to formthe container.